1. Field of the Invention
The present invention relates to a hydraulic circuit for a construction machine, which can implement an auto idle function by automatically reducing revolution of an engine when a working device of the construction machine such as an excavator is not driven.
More particularly, the present invention relates to a hydraulic circuit for a construction machine, which can minimize an energy loss of a hydraulic system by automatically reducing revolution of an engine when a working device such as a boom is not driven.
Hereinafter, in the accompanying drawings, only the construction of pilot signal lines related to an auto idle function is illustrated. When corresponding switching valves are switched over, the pilot signal lines are intercepted. The spool switching state of the switching valves and flow paths formed between the switching valves and working devices are not separately illustrated.
2. Description of the Prior Art
Referring to FIG. 1, a conventional hydraulic circuit for a construction machine having an auto idle function includes first to third hydraulic pumps P1, P2, and P3; a first switching valve A composed of valves installed in a flow path of the first hydraulic pump P1 and shifted to control hydraulic fluid fed to working devices, such as arm, boom, bucket, and the like; a second switching valve B composed of valves installed in a flow path of the second hydraulic pump P2 and shifted to control hydraulic fluid fed to working devices, such as arm, boom, option device, and the like; a third switching valve C composed of valves installed in a flow path of the third hydraulic pump P3 and shifted to control hydraulic fluid fed to a swing device and so on; a fourth switching valve D composed of valves installed on upstream sides of the flow paths of the first and second hydraulic pumps P1 and P2, respectively, and shifted to control hydraulic fluid fed to left and right traveling devices; and a confluence switching valve 8 installed on a downstream side of the flow path of the third hydraulic pump P3 and shifted to selectively supply the hydraulic fluid from the third hydraulic pump P3 to the working devices on the first hydraulic pump side P1 or the working devices on the second hydraulic pump side P2, in response to a pilot signal pressure Pi1 applied thereto.
In a small-sized excavator, the hydraulic fluid fed from the first hydraulic pump P1 is supplied to a right traveling motor and the hydraulic fluid fed from the second hydraulic pump P2 is supplied to a left traveling motor to drive the traveling motors. In the case of driving other working devices such as boom and so on, the confluence switching valve 8 is used to supply the hydraulic fluid fed from the third hydraulic pump P3 to the working devices.
The confluence switching valve 8 is shifted, in response to the pilot signal pressure Pi1 being supplied from a pilot pump to a signal line 3, to supply the hydraulic fluid fed from the third hydraulic pump P3 to the working devices on the first hydraulic pump side P1 or to the working devices on the second hydraulic pump side P2.
A signal line 4 connected to a signal line 3 includes a signal line 5 passing through the first and second switching valves A and B for the working devices and a signal line 6 passing through the fourth switching valve D for traveling devices. In the case where only either the first and second switching valves A and B or the fourth switching valve D is shifted to operate, no signal pressure is formed in the signal line 3.
In the case where the first and second switching valves A and B for the working devices and the fourth switching valve D for the traveling devices are simultaneously shifted to operate, the confluence switching valve 8 is shifted in response to the pilot signal pressure Pi1 formed in the signal line 3. Accordingly, the hydraulic fluid fed from the third hydraulic pump P3 is supplied to the working devices of the first hydraulic pump side P1 or the working devices of the second hydraulic pump side P2.
In the case of simultaneously implementing the above-described confluence function and the auto idle function, it is required to separately provide a signal line that can detect the shifting of the first and second switching valves A and B and the fourth switching valve D.
That is, if either the first and second switching valves A and B or the fourth switching valve D is shifted, no signal pressure is formed in the signal line 3. Accordingly, the pressure in the signal line 3 cannot be used as an auto idle signal pressure.
Accordingly, in the case of shifting the first and second switching valves A and B or the fourth switching valve D, a separate signal line 7 that can detect the shifting is required. The signal line 7 is connected to the signal line 3, and is connected to a flow path in which a second throttling part 2 is installed. In addition, the signal line 7 is constructed to pass through the first to third switching valves A, B, and C for the working devices and the fourth switching valve D for the traveling devices.
In a neutral state of the first to fourth switching valves A, B, C, and D, no signal pressure is formed in the signal line 7. Accordingly, it is judged that the working devices do not operate, and thus the engine revolution of the equipment is automatically reduced.
In the case of shifting any one of the first to fourth switching valves A, B, C, and D, the signal pressure is formed in the signal line 7, and thus the engine revolution can be accelerated by the signal pressure.
Referring to FIG. 2, another conventional hydraulic circuit for a construction machine having an auto idle function includes a confluence switching valve 8 shifted by a signal pressure Pi1 fed from a pilot pump (not illustrated) to a signal line 13 to supply hydraulic fluid fed from a third hydraulic pump P3 to working devices on a first hydraulic pump side P1 or working device on a second hydraulic pump P2; a signal line 16 which is connected to the signal line 13 and in which a signal pressure is formed when a fourth switching valve D for traveling devices is shifted; a signal line 15 which is connected to a signal line 16 and in which a signal pressure is formed when first and second switching valves A and B for working devices are shifted; and a signal line 17 in which a fourth throttling part 12 is installed, which is connected to a signal line to which a pilot signal pressure Pi2 is supplied, and in which a signal pressure is formed when the first to third switching valves A, B, and C for the working devices and the fourth switching valve D for the traveling devices are shifted.
The conventional hydraulic circuit of FIG. 2 further includes first to third hydraulic pumps P1, P2, and P3; a first switching valve A installed in a flow path of the first hydraulic pump P1; a second switching valve B installed in a flow path of the second hydraulic pump P2; and a third switching valve C installed in a flow path of the third hydraulic pump P3. However, since these constituent elements are substantially the same as those of the circuit as illustrated in FIG. 1, the detailed description thereof will be omitted. The same drawing reference numerals are used for the same elements across various figures.
As illustrated in FIGS. 1 and 2, the conventional hydraulic circuits having an auto idle function requires a confluence circuit including the confluence switching valve 8 and separate auto idle signal lines 7 and 17, and this causes the construction of the signal lines to be complicated. Particularly, the hydraulic circuit as illustrated in FIG. 2 has very complicated signal lines.
In addition, since the signal lines 7 and 17 pass through spools of the first to third switching valve A, B, and C for the working devices and the fourth switching valve D for the traveling devices, the hydraulic fluid may leak through joint surfaces of the first to fourth switching valves A, B, C, and D. Particularly, in a high-temperature working environment, the formed auto-idle pressure may become unstable due to the leakage of the hydraulic fluid.